Utility furnaces are used in various industries for a variety of different purposes. Common issues associated between these various industries include the handling of the by-products created by the combusted fuel. These byproducts can decrease the utility furnace efficiency and pose other pollution problems.
In one example, the pulverized coal, used in various types of boilers, burns in a combustion chamber. The hot gaseous combustion products then follow various paths, giving up their heat to steam, water and combustion air before exhausting through a stack. The boiler is constructed mainly of interconnected elements such as cylinders such as the super heater tubes, water walls, various larger diameter headers, and large drums. Water and steam circulate in these elements, often by natural convection, the steam finally collecting in the upper drum, where it is drawn off for use. Water/steam tubes typically almost completely cover the walls of the passage so that they efficiently transfer heat to the water/steam. As the coal is burned, ash and/or other products of combustion build-up on the tubes.
Presently soot blowers are available to aid in the removal of these build-ups. Soot blowers are mechanical devices used for on-line cleaning of ash and slag deposits on a periodic basis. They direct a pressurized fluid through nozzles into the soot or ash accumulated on the heat transfer surface of boilers to remove the deposits and maintain the heat transfer efficiency. The soot and dust generated in combustion get deposited on outer tube surfaces. This adds to the fuel requirements to maintain utility furnace temperatures. Running with added fuel in turn increases deposition of byproducts of fuel burning and also increases the chances of the tubes failure by overheating. This eventually results in shutting down of the furnace for repairs. All this can be avoided by soot blowing. Regular soot blowing saves fuel and boiler downtime. In other words steam at constant parameters is available over a longer period of time. Numerous types of soot blowers exist including but not limited to wall soot blowers, long retractable soot blowers, rotating element soot blowers, helical soot blowers, and Rake-type blower. Under optimal conditions this ash is removed from the surface of the tubes by pressured fluid (typically air, saturated steam or super-heated steam) delivered soot blowers. However under suboptimal conditions the ash melts due to reaching its fusion temperature and results in the formation of slag. Soot blowers are less effective at removing the slag.
The major problem with the formation of slag is that it insulates the elements, thus requiring the furnace to burn at a hotter temperature to create the same increase in water temperature. Excessive ash deposits on a coal-fired boiler's heat transfer surfaces will reduce its efficiency, and in extreme cases a boiler can be shut down by ash-related problems. Slagging incidents are a heavy drag on the global utility industry due to reduced power generation and equipment maintenance.
The changing electricity market and political pressures have pushed the use of fuels other than coal. For example, use of gas, biofuel, co-fired fuel, etc., has become widespread. These factors have led to coal-fired plants being operated under unusual loads. This change in operation has altered the effects of boiler slagging. The co-firing of other fuels with coal, especially biomass, represents a large challenge to utility furnace operation. The ash chemistry of these alternative fuels is often very different to that of the coals and has given rise to serious problems. The tendency of coal for slagging depends on its composition. The complex interaction between a boiler's operating conditions and the fuel chemistry makes the prediction of slagging difficult. Furthermore, the increasing pressure on coal-fired power stations to reduce emissions has led to the development of technologies for the abatement of specific pollutants that impact on ash slagging. The new generation of pulverized coal fired plant, designed for high efficiency through the use of high steam temperatures and pressures, present further challenges with respect to ash slagging and fouling.
Various methods of removing the slag other than with a soot blower are in use. For example in some power plants, engineers fire shotguns into the furnace to break the slag off of the pipes. Other methods require taking the furnace off line to deal with the problem. These techniques are less than satisfactory, and neither of these solutions address issues of pollution.
In dealing with the byproducts released into the environment (pollution), various systems associated with the utility furnaces process the byproducts before their release. However, better methods of chemical processing of these byproducts are constantly sought after. New utility furnaces are almost certain to be required to operate under conditions that facilitate carbon capture and storage, for compliance with climate change driven requirements. While such requirements are frequently sought in relation to coal fired furnaces they could also apply to a variety of fuel types.
While the problems and limitations of utility furnaces are clear, there are few solutions. The presence of certain compounds in the utility furnaces have been experimented with and resulted in improved abilities to deal with slag and pollution. While the specific compounds vary across the board depending on the specific chemistry of the fuel and problem to be addressed, one uniform problem exists, there is no adequate delivery mechanism to inject the compounds into targeted spots in the furnace.
A solution to the problem of delivering various compounds to targeted locations of a utility furnace is needed. As such a solution to the delivery of compounds into a utility furnace is presented herein.